The evolution of diagnostic endoscopy toward surgical endoscopy has raised new requirements that must be met by the devices and instruments used. Medical irrigating and aspirating devices belong to this category of equipment.
Initially made for dilating the cavity under observation, then used more recently to dynamically create an "aseptic operating space," these devices had to adapt their characteristics to therapeutic means used by endoscopic surgeons, means that require fast reaction to ensure the safety of the patient.
Peristaltic pumps comprising a flexible transfer tube successively pinched by rollers moving one behind the other in an orbit, in particular rollers carried by a rotor, are frequently used for the transfer and the pressurizing of corrosive or sterile liquids. Whatever their form and the number of rollers, current peristaltic pumps only require that at any instant only two of the rollers be active. The closed space inside the tube of the pump delimited by these two rollers forms the liquid-transfer chamber.
Peristaltic pumps are the preferred type for medical applications, in particular in devices for circulation outside the body or in devices for irrigating surgical cavities, as in urology or arthroscopy where these pumps are now in use. By way of example of the known type of medical device using a peristaltic pump, one can cite the surgical irrigating and aspirating device described in French 2,642,297 and WO 90 08562. Nonetheless these peristaltic pumps available on the market generally deliver a cyclic flow having instantaneous flow variations that can exceed 20 to 30% of the average flow of these pumps. This is shown schematically in the diagram of FIG. 1 where time t is on the abscissa and flow D is on the ordinate.
These flow variations are the result of the variations of volume of the transfer chambers as the rollers disengage and in a more accessory manner of the compression of the transfer tube created by these rollers. Such flow variations can be a considerable inconvenience in surgical applications so that manufacturers of peristaltic pumps resort to the use of pressure-regulating or--smoothing devices at the pump output. These devices are normally passive and are not generally effective except for a given cadence, thus for a relatively restricted range of operation.
U.S. Pat. No. 3,726,613 proposes to suppress the variations of the cyclic flow by a peristaltic pump and an "active" device having a pressurizing element acting variably with respect to time on the transfer tube at the outlet of the pump under the control of an operating device which itself has a cam fixed to the rotor of the pump and acting via an oscillating link on the pressurizing element. This document contains an accurate analysis of the physical problems of the problem, but it describes a solution that, using "active" elements, is mechanically fairly complex and relatively expensive.
In German utility model 94 122 28 there is also a peristaltic pump which attempts to smooth the output flow by means of a widened space of continuously increasing width between the rotor and the stator, from the input to the outlet of the pump in the direction defined by the movement of the rollers. This configuration results in an eccentric orientation of the circular recess of the stator relative to the axis of the rotor.
In any case this document does not explain how the device in question functions and the proposed solution does not appear to work in principle or practice. At least the operation of this device seems to rely on the simultaneous cooperation of a high number of rollers of the rotor with the tube which supposes a deep recessing of the rotor into the stator having as a result difficulties of completely and quickly disengaging the rotor from the stator.